An oxide of cerium could protect against UVA rays in the same way as the inorganic filters zinc and titanium, according to researchers in France. Thierry Devers and his team from the University of Orleans have been researching the potential of cerium, one of the rare earth metals, as a UV filter.

Calcium improves protection

In its pure form, cerium dioxide only blocks out rays at the higher end of the UVA spectrum. However, Devers and the team have found that adding calcium to the cerium dioxide makes it effective against lower wavelengths of light. In fact the addition of calcium reduces the size of the particles, Devers said.

This has two effects, according to the scientist. Primarily, it means that the material blocks shorter wavelengths of light and can therefore protect against the full UVA spectrum. In addition, as the smaller particles can spread more evenly across a surface it improves the material’s ability to reflect UVA rays. According to Devers, the bigger the percentage of calcium, the smaller the particles, and the team will be looking to see if there is a limit to this effect.

There remains a lot to be done, according to Devers, including exploring in more detail the effect of the calcium on the protection provided by the material and investigating the SPF factor that it could provide. “However, the biggest thing that remains to be explored, and that we hope to do with an industry partner, is to investigate the formulation possibilities of the material. We need to look at whether the material is suitable for oil, water or cream bases, and whether or not it mixes well with titanium dioxide, before we can start looking at the SPF,” he said.

An alternative to zinc oxide

According to Devers, cerium dioxide could, theoretically, replace zinc oxide, a widely used inorganic filter. Although zinc oxide is accepted for use in many countries, Devers notes it is not yet included on the European Cosmetics Directive positive list. He maintains that if zinc oxide does not get accepted as a UV filter by the Directive, a company that had already started investing in a potential substitute would have a significant head start on the rest of the industry.

The U.K. cosmetics trade association the CTPA confirmed that an application has been made for the inclusion of zinc oxide into Annex 7—the positive list for UV filters—but this has not yet been granted.

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